A stunning example of an iridescent ammonite fossil of the species Caloceras johnstoni from North Somerset, UK.
The piece of thin limestone matrix measures 145 mm (5.75 inches) across and contains a single partial ammonite that measures 80 mm (3.2 inches), which is large for this species.
The ammonite is very well preserved and has been prepared out of the rock to reveal the shell, which displays some stunning iridescent colours that change depending on the angle that the fossil is viewed at. There is a beautiful mix of red, green, blue, and orange colours in the shell - making some of the strongest colours possible in these fossils. There is also a small unusual bivalve shellfish that attached itself onto the inner whorls of the ammonite. It weighs 285 grams.
Around 200 million years old (Hettangian, Early Jurassic), this fossil would make a wonderful addition to any collection. These fossils are preserved in the same way as the more famous Canadian "ammolite", which is turned into valuable gemstones due to the stunning iridescence.